We are investigating the molecular basis of the energy coupling mechanism by which cells use metabolic energy to accumulate nutrients. For this purpose we are using the simple homofermentative lactic acid microbe, Streptococcus faecalis as a model system. There is now much evidence that the membrane bound ATPase in this organism is a coupling factor in the energized transport of K ions and amino acids. The major objective of our work currently is to characterize as fully as possible the ATPase and the membrane proteins with which the enzyme is associated. To this end we are continuing our investigations on the ATPase subunit structure, the factors involved in membrane binding of the enzyme, and the properties of the tightly bound non-exchangeable ATP ligands in the ATPase. BIBLIOGRAPHIC REFERENCES: A. Abrams, C. Jensen and D. Morris. Studies of Substructure and Tightly Bound Nucleotide in Bacterial Membrane ATPase, J. Supramolecular Structure, 3, 261-274 (1975). A. Abrams, Structure and Function of Membrane-Bound ATPase in Bacteria in "The Enzymes of Biological Membranes" (A. Martonosi, Ed.) Plenum Press, N.Y. (1976) in press.